Definition:

Stage I is divided into stages IA and IB, depending on where the cancer is found. In stage IA, cancer has formed in the mucosa or submucosa layer of the esophagus wall. The cancer cells are grade 1 or 2. Grade 1 and 2 cancer cells look more like normal cells under a microscope and grow and spread more slowly than grade 3 cancer cells. In stage IB, cancer has formed (1) in the mucosa or submucosa layer of the esophagus wall, and the cancer cells are grade 3. Grade 3 cancer cells look more abnormal under a microscope and grow and spread more quickly than grade 1 and 2 cancer cells; or (2) in the mucosa or submucosa layer and spread into the muscle layer of the esophagus wall, and the cancer cells are grade 1 or 2.